Method in a sheet metal work center and a sheet metal work center

ABSTRACT

The invention relates to a sheet metal work center and a method for fabricating sheet metal therefrom. In the sheet metal work center, a locking arrangement is placed between the upper tool and a releaser, and the transfer device is arranged to consist of two parts. The sheet metal work center is adaptable to work in either a passive or active mode. In the passive mode, the releaser is positioned at a certain distance from the surface of the sheet, and the movements of the upper tool and the releaser are made with the locking arrangement locked and either part of the transfer device used. In the active mode, the releaser is positioned to be in contact with the sheet, and the movements of the upper tool and releaser are made with the locking arrangement locked and either part of the transfer device used. Working operations of the lower tool are conducted with the locking arrangement released and a part of the transfer device used, and the releaser being kept at its position by a second part of the transfer device.

FIELD OF INVENTION

The invention relates to a method of implementing a working process atsubstantially the same working speed irrespective of whether an activeor passive mode is used to fabricate a worksheet in a sheet metal workcenter.

BACKGROUND OF INVENTION

Generally in sheet metal working technology, for example in sheetpunching, certain components are always needed. These include tools,punches or drifts, a releasing plate or a releaser or stripper, and acushion. In sheet punching, the machining is conducted in a way that apunch is used to make a hole in a sheet against the cushion, and thepunch is drawn out of the hole either by a spring force or by anotherforce, wherein the releasing plate prevents the punched sheet fromrising with the punch, the plate remaining in its place. In sheetpunching, there are two possibilities to conduct the machining: first ofall in a way that the releasing plate is in contact with the sheet to bepunched during each punching stroke; or the second alternative beingthat there is a certain air gap between the material to be punched andthe releasing plate. Each method has its own advantages, i.e., whenthere is a contact with the plate at the punching stage, the plate willnot vibrate during machining. On the other hand, when punching aluminiumor materials which are soft or have a sensitive surface, the releasingforce may become too great and leave scratches on the surface of thematerial. Because of this, it is preferred that both alternatives beavailable in a sheet metal work center. Thus the releaser plate could bekept in place during the punching strokes to achieve a permanent airgap, or the releaser plate could touch the material with every punchingstroke.

Known sheet metal work centres use a single-tool system having a buffer,to which the drift is mechanically fixed, wherein it can be exchanged,if necessary, either manually, by a robot or with a manipulator, and areleaser plate, wherein both are controlled with a separate pressurizedmedium cylinder arrangement. This kind of a solution involves, however,the problem that two separate shaft systems are required for controllingthe pressurized medium, and these must be synchronized with a numericalcontrol (NC) unit. This tends to delay the working process. Thesingle-tool system is relatively fast in the so-called passive mode,wherein the releaser, usually a releaser plate, is stationary at thedistance of an air gap from the sheet to be worked during the punchingstroke. Thus the buffer, with the drift, can conduct punching strokeseven at very short intervals. The problem is present particularly whenthe so-called active mode is used, wherein the releaser plate is placedin contact with the surface of the sheet to be worked. Thus a need forso-called serial control arises, wherein the implementation of the NCcontrol unit requires first the information that the releaser plate isin contact with the surface of the sheet to be worked before the buffercan be given a punching command. This fact will cause a delay of aboutone third in the working process when moving from the passive mode tothe active mode.

SUMMARY OF THE INVENTION

With the present invention, it is possible to implement the workingprocess substantially at the same working speed irrespective of whetherthe active or passive mode is used, i.e. whether the releaser plate isat a distance of an air gap from the sheet to be worked or in contactwith said plate. Using the solution of the invention, theabove-mentioned working operations can be conducted with so-calledone-shaft control. The purpose of the invention is thus to raise thestandard of prior art and to present new surprising solutions for makingthe operations of sheet metal work centers more efficient and varied.

The method of the invention is primarily characterized in what will bepresented in the characterizing part of the appended Claim 1.

The invention is also related to a sheet metal work center. Its primarycharacterizing features are disclosed in the characterizing part of theappended independent claim on a sheet metal work center.

The appended dependent claims disclose some advantageous embodiments ofthe sheet metal work center according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail in the followingdescription with reference to the embodiment shown in the appendeddrawings, wherein:

FIG. 1 is a schematic general view of a sheet metal work centeraccording to the invention, shown in a vertical section,

FIG. 2 is a schematic illustration of the principle of the invention,shown in steps a to e,

FIG. 3 illustrates an embodiment of the buffer structure in verticalcross-section,

FIG. 4 shows the stopper structure in vertical cross-section,

FIG. 5 shows the buffer and stopper structures seen from the side,

FIG. 6 is a flow chart illustrating the operating principle of thebuffer structure, and

FIG. 7 is a hydraulic chart for using the buffer and stopper structures.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1, the reference numeral 1 indicates the machinebody of the sheet metal work center, having a buffer structure 2 placedin its upper part and a stopper structure 3 placed in its lower part.The machine body has either a closed, circumferential O-structure or anopen structure having e.g. a C-, J-form or the like. FIG. 1 shows alsoequipment related to the buffer transfer device indicated with thereference numeral 4, such as a hydraulic accumulator 4a and a valveblock 4b. The sheet 5 to be worked is placed onto the work table or themachining level 6, underneath the upper tool or drift 7 and the releaser13, and above the lower tool or stopper 8 in the stopper structure 3,between said parts 7, 13,and 8. Sheet 5 is held (fixed) and moved bymeans, such as for example the carriage and clamps disclosed in U.S.Pat. No. 4,658,682, along machining level 6 for processing. Such meansis represented by the dotted carriage 5a. The sheet metal work centercan be used for working at least the following operations: punching,forming, screwing, and other generally known working operations to beconducted with a sheet metal work center. Normally, the buffer structure2 conducts the sheet punching operations with a downwards directedworking movement. Alternatively, the lower tool 8 can be used forforming, wherein the working direction of the forming lower tool 8 isfrom below upwards.

FIG. 2 shows steps a to e illustrating schematically some work stages tobe conducted with the sheet metal work center. A punch stroke indicatesin this context the work cycle of the buffer 10 and the upper tool 7,including the working operation and the return movement to the startingposition.

FIG. 2a shows the buffer structure 2 and the stopper structure 3 in thatdrift exchange position, in which the upper tool 7 is exchanged in thebuffer structure 2, and the releaser 13 and the stopper structure 3 inthat position, in which the lower tool 8 is exchanged. The bufferstructure 2 comprises as main parts a buffer fixing body 9, at which thebuffer structure 2 is fixed to the machine body 1. Further, the bufferstructure 2 comprises a buffer 10 and an auxiliary transfer body 11effective outside the buffer 10, both being coupled to the buffer fixingbody 9 by means of a transfer device 12. Furthermore, the lower part ofthe buffer structure 2 is provided with the upper tool 7 and thereleasing plate or releaser 13 surrounding the upper tool 7 and beingconnected with the auxiliary transfer body 11 by means of the transferdevice 14 of the releaser 13. Moreover, the buffer structure 2 comprisesa locking arrangement 15 effective between the buffer 10 and theauxiliary transfer body 11, for locking the buffer 10 and the auxiliarytransfer body 11 in relation to each other at certain work stages.

The transfer device 12 comprises as its first part a buffer transferdevice 12a, effective between the buffer 10 and the buffer fixing body9, and as its second part a transfer device 12b for the auxiliarytransfer body 11, effective between the auxiliary transfer body 11 andthe buffer fixing body 9.

The stopper structure 3 comprises as its main part a stopper fixing body16, at which the stopper structure 3 is fixed to the machine body 1. Thestopper structure 3 comprises a stopper transfer device 17 arranged tobe movable in the vertical direction in relation to the stopper fixingbody 16. The upper part of the stopper transfer device 17 is providedwith the lower tool 8, fixed in a releasable manner with a tool fixingmeans 18.

FIG. 2b shows the starting position for a punching stroke, wherein thebuffer 10 and the auxiliary transfer body 11 with the means connected toit are moved in connection with the sheet 5 in a way that the releaseris placed at a distance of air gap 19 from the top surface of the sheet5. Thus the work levels 20, 21 of the upper tool 7 and the releaser 13are substantially at the same level. At this stage, the control unit ofthe sheet metal work center can be used to make a selection between aso-called passive punching stroke, wherein the releaser will remain atthe distance of said air gap 19 from the sheet 5, and a so-called activepunching stroke, wherein the releaser 13 is brought into contact withthe top surface of the sheet 5. The operations of this selection will bedescribed in detail with reference to FIG. 6.

FIG. 2c shows the stage of making a passive punching stroke, wherein thetransfer device 12b of the auxiliary transfer body is locked to bestationary in relation to the buffer fixing body 9 and the releaser 13remains in its position, maintaining the distance of the air gap 19 tothe sheet 5. The locking arrangement 15 effective between the buffer 10and the auxiliary transfer body 11 is released, wherein the buffertransfer device 12a can conduct a downwards directed work movement inrelation to the auxiliary transfer body 11 and the buffer fixing body 9.

FIG. 2d, in turn, shows the stage of making an active punching stroke,wherein the locking arrangement 15 between the buffer 10 and theauxiliary transfer body 11 is locked and the transfer device 12b of theauxiliary transfer body is released, wherein the unit comprising thebuffer 10 and the auxiliary transfer body 11 with the means related toit can be moved downwards by the buffer transfer device 12a. When thereleaser 13 meets the surface of the sheet 5, the releaser transferdevice 14 will yield for the auxiliary transfer body 11, producing acounter-force for the release of the upper tool 7 at the end of thebuffer 10. One function of the transfer device 14 of the releaser 13 isparticularly to generate an adjustable releasing force. FIG. 2d shows asituation, in which the upper tool 7 has punched the sheet, penetratingunder the upper surface of the lower tool 8 of the stopper structure 3within the scope of the adjustable stroke length. FIG. 2e, in turn,shows the use of the sheet metal work center in forming, wherein thestopper structure 3 is used as the forming tool and the buffer structure2 correspondingly as the stopper. Thus the upper tool 7 and the uppertool fixing means are removed from the buffer 10. The forming tool orthe buffer 22 is fixed to the tool fixing device 18 in connection withthe stopper structure 3. The releaser 13, or in this case the formingstopper, is lowered by using the second part 12b of the transfer deviceto the lowest position in connection with the sheet 5 to be worked, asshown in FIG. 2e, to effect a counterforce to the forming work. Thereleaser transfer device 14 is driven to a position in which thereleaser transfer device 14 can yield in relation to the auxiliarytransfer body in a direction perpendicular to the main level of thesheet to be worked.

In an advantageous embodiment, the buffer structure 2 is a substantiallycylindrical form piece, wherein the buffer fixing body comprises acentral hole, in which the substantially tubular auxiliary transfer body11 is inserted. The buffer 10, in turn, has a primarily rod-likestructure. All of the parts 9, 10 and 11 comprise constructive parts,which can be used to constitute the embodiment of buffer structure 2shown in FIG. 7, using pressurized medium, particularly hydraulic fluid.

With particular reference to FIG. 3, the buffer 10 is further arrangedto be rotary around the central axle in alignment with the bufferstructure by means of a rotating device 23 arranged in the upper part ofthe buffer structure 2. The buffer 10 is formed to have a hollow upperpart comprising spaces 25a, 25b for pressurizing medium in a cylindricalhole 25 in the axial direction, wherein a stationary piston 26 fixed tothe top cover 24 of the buffer fixing body 9 is placed in the hole 25.The top cover 24 is connected with a channel system 27a in thelongitudinal direction of the piston 26, through which system thepressurized medium is led to the stationary piston 26 and further to thepressure space 25a, which is limited by the front surface 26a of thestationary piston 26 and the bottom 29 of the pressurized medium space25a. A second channel system 27b, partly aligned with the stationarypiston 26, is connected in the radial direction to the pressurizedmedium space 25b formed with the help of an insert 28. Theabove-mentioned structure constitutes a cylinder operating on theso-called differential principle. The length of the insert 28 (maximumdistance between the radial surfaces 25c and 26b) in the longitudinaldirection of the buffer 10 determines the maximum movement length ML ofthe buffer. The end surfaces of the insert 28 consist firstly of theradial surface 26b of the contraction of the stationary piston 26 andsecondly of the radial surface 25c of the contraction of the hole.

On the outer surface of the buffer 10, between the buffer 10 and thebuffer fixing body 9, a tooth wheel rim or a corresponding rotatingmeans 23a is mounted on bearings 23c, driven by a worm pipe or acorresponding driving means 30, which in turn is mounted on bearings onthe buffer fixing body 9. The above-mentioned gear arrangement, which inFIG. 3 is indicated with the reference numeral 42, is used to rotate thebuffer 10 in relation to the buffer structure 2 around the vertical axleto achieve the desired angular position of the drift. The workingmovement of the buffer 10 is achieved by the pressurized medium suppliedinto the pressure space 25a, wherein the bush-like tooth wheel rim 23asurrounding the outer surface of the buffer 10 is arranged in relationto the fixing body 9 of the buffer 10 in a way that the necessaryrelative movement in the longitudinal direction of the buffer 10 takesplace between the inner surface of the tooth wheel rim 23a and the outersurface of the upper part of the buffer 10 during working and returnmovements of the buffer 10 (surface 31). For transmission of therotating force, a wedge part 23b is provided between the parts 10 and23a. Thus, the unit presented above constitutes the transfer device 12aof the buffer 10 (FIG. 2).

In the lower part of the buffer structure 2, in turn, the transferdevice 12b of the auxiliary transfer body 11 is arranged. It consists ofan annular pressurized medium space 34 formed in the longitudinaldirection of the buffer structure 2, between the auxiliary transfer body11 and the buffer fixing body 9. Thus the outer surface of the auxiliarytransfer body 11 is provided with an annular protruding flange 32, whosefront surfaces 33a, 33b face said pressurized medium space 34. In acorresponding manner, the buffer fixing body 9 is provided with anoutwards facing annular recess 35, whose front surfaces 36a, 36b facesaid pressurized medium space 34. The flange 32 is movable in thelongitudinal direction of the buffer structure 2 in the recess 35. Withthe pressurized medium space 34, pressurized medium connectors, such asdrillings or the like 37a and 37b, are provided, wherein the effect ofthe pressurized medium can be turned to the front surfaces 33a, 33b ofthe flange 32 in the auxiliary transfer body 11.

The locking arrangement 15 between the buffer 10 and the auxiliarytransfer body 11 is formed after the buffer transfer device 12a in thelongitudinal direction of the buffer. The buffer 10 is composed of twoparts so that the circumference of its upper part is greater than thecircumference of its lower part, wherein a radial front surface 38a isformed between said parts, forming part of the locking arrangement 15.In a corresponding manner, the auxiliary transfer body 11 is providedwith an annular front surface 38b to make an annular pressurized mediumspace 39 in the axial direction. In the pressurized medium space 39, arotary piston 40 is arranged, pressed on its axial surfaces on one handagainst the outer surface of the lower part of the buffer 10 and on theother hand against the inner surface of the upper part of the auxiliarytransfer body 11. The pressurized medium space 39 is connected via apressurized medium connector 41 to the pressurized medium supply. InFIG. 3, the rotary piston 40 is shown in a position in which the buffer10 is free to move the distance VM (free distance) in relation to theauxiliary transfer body 11. Thus the annular piston 40 is moved with thebuffer 10, wherein the pressurized medium on the side of its frontsurface 43 is removed via the connector 41. This generates a downwardsdirected movement of the upper tool 7 in relation to the releaser 13.The lower part of the buffer 10 is equipped with a tool exchangemechanism which is generally indicated with the reference numeral 47. Atool locking mechanism 48 comprises the combination of a lower chuck 49,a rod 50 and a piston part 51. This combination is placed incorresponding cylindrical drillings in the buffer 10 in the longitudinaldirection. The upper part of the locking mechanism 48 is placed inpressurized medium space 52, wherein the lower surface of the pistonpart 51 is provided with locking by the pressurized medium at a pressureeffective through pressurized medium connector 53a, wherein the lockingmechanism 48 moves to its upper position shown in FIG. 3. In acorresponding manner, when effective through pressurized mediumconnector 53b, the locking mechanism moves to its lower position in thelongitudinal direction of the buffer 10, wherein the upper tool 7 can beexchanged. The auxiliary transfer body 11 is penetrated by pressurizedmedium channels 44 and 45, through which the pressurized medium is ledto the pressurized medium connectors 53a and 53b, respectively. Thepressurized medium channels 44 and 45, like the pressurized mediumconnector 41, are placed in projections 46a (parts 44 and 45) and 46b(part 41), which are placed in corresponding axial grooves 9a and 9b,respectively, in the buffer fixing body 9. The lower part of the lowerchuck 49 of the locking mechanism 48 is provided with a recess 54holding a fixing adapter 55, and this is connected with an intermediateadapter 56 underneath the fixing adapter 55 and within the sleeve-likereleaser 13. The fixing adapter 55 comprises a rod part extending in thelongitudinal direction of the buffer 10 and having on its outer surfacea threading which is placed in the threaded hole in the upper tool 7,wherein the upper tool 7 can be tightened against the lower frontsurface of the intermediate adapter 56 (screwing not shown in FIG. 3).

FIG. 3 shows further the transfer device 14 of the releaser 13 whosegeneral functions were described with reference to FIG. 2. The lowerpart of the auxiliary transfer body 11, the inner surface of its tubularform, is provided with a recess 100 in the longitudinal direction of thebuffer structure. The buffer 10 is surrounded by the sleeve-like framepart 101 of the transfer device 14. The upper part of the frame part 101is provided with a flange part 102 movable in the recess 100. The lowerpart of the frame part 101 contains a groove-like ring clip 103 insidethe sleeve form for fixing the releaser 13. The releaser 13 consists ofa releaser plate 13a parallel to the main level of the sheet to beworked, a sleeve-like releaser frame 13b adjacent to its outer edge inthe axial direction, and a flange 13c protruding in the radial directionfrom the upper edge of the releaser frame and placed in the ring clip103. The releaser 13 can, in connection with the exchange of the tool 7,be exchanged e.g. by a manipulator. The recess 100 forms a pressurizedmedium space 104, into which and from which the pressurized medium isled via a channel system 105 penetrating the auxiliary transfer body 11to the pressurized medium connector 106 in the buffer fixing body 9.Between the buffer fixing body 9 and the buffer 10, an annular space 107is formed in the longitudinal direction of the buffer structure 2,making it possible to maintain the pressurized medium connection betweenthe pressurized medium connector 106 and the end 108 in connection withthe annular space 107 of the channel system 105.

With reference to FIG. 4, the stopper structure 3 comprises firstly astopper fixing body 16, at which the stopper structure 3 is fixed to themachine body 1 of the sheet metal work center. The fixing body 16 hasadvantageously the form of a cylindrical piece, whose mantle 58 hasinner or central hole 59 which holds the tool fixing body 60 which ishydraulically arranged to move, if necessary, in the longitudinaldirection of the central hole 59 of the stopper fixing body 16 and inthe vertical direction with the transfer device 17, particularly itshydraulic cylinder-piston combination 61 which is placed in the lowerpart of the stopper structure 3 as an extension of the tool fixing body60. Both the tool fixing body 60 and the piston rod 62 of the transferdevice 17 formed as an extension thereof are primarily hollow, tubularform pieces.

The upper part of the tool fixing body 60 is provided with the fixingdevice 18 of the lower tool or the stopper 8. When the sheet metal workcenter is used for forming, the lower tool is a buffer (cf. FIG. 2e).

In accordance with the invention, the tool fixing body 60, the lowertool 8 and the fixing device 18 can be placed by the cylinder-pistoncombination 61 in several height positions in relation to the stopperfixing body 16 and the working level 6 (cf. FIG. 1). In the lowerposition (situation A), the lower tool 8 is accessible in the so-calledexchange position underneath the lower surface of the working level 6,wherein the lower tool 8 can be exchanged e.g. by a manipulator, or itcan be serviced. Secondly, in the so-called middle position (situationB) the upper surface 8a of the lower tool 8 is substantially at thelevel of the upper surface of the working level 6 (cf. FIGS. 2b-d). Thusparticularly the buffer structure 3 can be used for different formingoperations, the lower tool 8 being the stopper. Thirdly (situation C),the lower tool can be used for forming work as shown in FIG. 2e, whereinthe upper surface 8a of the buffer 8 used as the lower tool passes theupper surface of the working level 6 in the vertical direction.Fourthly, the cylinder-piston combination makes it possible to re-adjustthe position of the lower tool 8, which is needed because of wearing andre-grinding, in a very simple way. Also the disadvantages of noise andvibration are reduced, because the working strokes have an impact on thehydraulic pressurized medium and not directly on the machine body.

The embodiment shown in FIG. 4 is formed in a way that thecylinder-piston combination 61 of the transfer device 17 comprises arecess 70 formed on the surface of the inner hole 59 of the stopperfixing body 16 in the longitudinal direction of the stopper structure 3.The ends 63, 64 of the recess 70 are provided with pressurized mediumconnectors 65, 66 penetrating the stopper fixing body 16. In the upperpart of the piston rod 62, there is a flange 67 forming the actualpiston, its radial front surfaces 68, 69 facing the ends 63 and 64. Thearea of the lower front surface 69 is greater than the area of the upperfront surface 68, because a greater force is required upwards thandownwards. Thus the diameter of the tool fixing body 60 can be greaterthan the diameter of the piston rod 62, wherein the flange 67 has agreater diameter than both the tool fixing body 60 and the piston rod62.

The surfaces 64 and 69 are substantially close to or facing each otherin the situation A. In the position shown in FIG. 4, i.e., when theflange 67 is at the middle section of the recess 70, the operation iseither in situation B or moving to situation C, in which the surfaces 63and 68 are substantially close to each other in a way that an excitationpressure space is left therebetween (as in situation A), as also whenthe surfaces 64 and 69 are close to each other.

When the surfaces 64 and 69 are approaching each other, i.e., when theoperation is close to situation A, the fixing pressure is released fromthe pressurized medium space 75 through the pressurized medium channelsystem 73 in the stopper fixing body 16 and through the pressure channelsystem 74 in the tool fixing body. A mechanical contact is formedbetween a lockpin cam 78 and the stopper fixing body 16 (surfaces 16aand 18a, i.e. the upper front surface of part 16 and the lower surfaceof the flange part of part 18), wherein the fastening of the lower tool8 is detached between the outer surface of an axial projection 91 on thetool fixing body 60 and the inner hole 92 in the lower tool 8. Thepressure channel system 74 is connected with the pressurized mediumspace 75 which is effective between the tool fixing body 60 and the toolfixing device 18 and is used for the hydraulic locking of the lower tool8 in connection with the stopper structure 3.

At this stage, the front surfaces 76 and 77 (the lower front surface 76in the tool fixing device 18 and the upper front surface 77 in the toolfixing body 60) are moved in the axial direction (against each other inthe longitudinal direction of the stopper structure 3) and the volume ofthe pressurized medium space 75 is reduced to the excitation volume.Thus the locking of the lower tool 8 is released, and it can be detachedin the lateral direction (perpendicular to the main level of FIG. 6)from the retaining structure of the lockpin cam 78 (in the fixing device18) and the groove 79 (in the lower tool 8) for example manually or byusing a manipulator. After the exchange of the lower tool 8, the toolfixing body 60 is moved upwards by using the cylinder-piston combination61, wherein by using the pressurized medium connection between the parts73 and 74, the pressurized medium space 75 is pressurized during therelative movement between the parts 16 and 60, wherein the pressurizedmedium fills up and thereby enlarges the pressurized medium space 75.The mechanical contact between the parts 16 and 18 is maintained, untilthere is a mechanical contact between the surfaces 8b and 80. The lowertool 8 is locked by an axial force effective between the upper frontsurface 80 of the tool fixing body 60 and the lower front surface 8b ofthe lower tool 8 from the pressurized medium space 75. The force betweenthe surfaces 8b and 80 is transferred via the lockpin cam-groovestructure 78, 79.

In structural respects, the pressurized medium space 75 is formed intothe inner hole 81 of the bush-like fixing device 18 of the lower tool 8as a recess 82 having the above-mentioned radial front surface 76. In acorresponding manner, the outer surface of the tool fixing body 60 isprovided with a recess whose upper radial front surface is theabove-mentioned front surface 77.

In the lower part of the stopper structure 3, between the stopper fixingbody 16 and the piston rod 62, a device 84 is placed for rotating thelower tool 8, being part of the transfer device 17, wherein the pistonrod 62 is surrounded by a bush-like tooth wheel rim or a correspondingrotary means 85, mounted on bearings 88 in the stopper fixing body 16. Adriving means, such as a worm pipe 86, for driving the tooth wheel rim85 is mounted on bearings on the stopper fixing body 16. The tooth wheelrim 85 is coupled to be dead in relation to the piston rod 62 with asliding key 87 which makes possible the axial movement of the rotatingdevice 84 and the piston rod 62 in relation to each other in thelongitudinal direction of the piston rod 62. The rotating device 84,which is substantially similar to the rotating device 23 in the buffer10 and also driven with an electric engine (not shown in the figures),is driven to bring the lower tool 8 used at the time to the desiredworking position in the radial direction of the lower tool.

FIG. 4 shows a group of packings 83 which are naturally needed betweenconstructively movable parts in hydraulic applications.

FIG. 5 shows the parts corresponding to the structures of FIGS. 3 and 4seen from the side and indicated with the reference numerals of FIGS. 3and 4 for the respective structural parts. In FIG. 5, the referencenumeral 89 indicates the position detector of the auxiliary transferbody.

FIG. 6 is a flow chart showing the operating principle of the bufferstructure and the selection between active and passive mode, with briefexplanations. The flow chart clarifies and supplements the descriptionpresented above.

Further, FIG. 7 is a diagram showing the hydraulic control system of thepressurized medium in the buffer and stopper structures. In FIG. 7, thereference numerals used indicate the same parts as before, whereapplicable. In this respect, reference is made to the above description.

The hydraulic system of FIG. 7 comprises a driving aggregate 120 forproducing the hydraulic pressure in the system. The aggregate isconnected via normal hydraulic pipes to the valves controlling theactuators valve 124 for tool change and valve 125 for the lockingarrangement.

The system comprises a hydraulic accumulator 121 and a servo valve 122controlling the buffer 10. The actual punching operation is effected bya differential cylinder used as the transfer device 12a of the buffer 10and comprising parts 25a, 25b, 27a, 27b and 122. For the operation ofthe differential cylinder, it is essential that the pressurized mediumspace 25b is always under systemic pressure and the pressurized mediumspace 25a is under the pressure corresponding to a balanced situation.The pressure in the pressurized medium space 25a is controlled with theservo valve 122.

The system comprises further a releasing force control system 123,consisting of pressure control valve 123a, venturi 123b and hydraulicaccumulator 123c. The purpose of the control system 123 is to controlthe releasing force when operating in the active mode. The pressurecontrol valve 123a is used to adjust the pressure setting value of thepressure space 104. The releasing force is directly proportional to thepressure in the pressure space 104. By means of the venturi 123b and thehydraulic accumulator 123c, the pressure in the pressure space 104 iskept constant irrespective of the volume of the pressure space 104.

Valves 126 and 127 are used for controlling the operation of theauxiliary transfer body 11. Using a free circulation valve 127, thepressurized medium connectors 37a and 37b can be connected with eachother, wherein the auxiliary transfer body 11 is released in the activemode. When the free circulation valve 127 is in a position that there isno pressurized medium connection between the pressurized mediumconnectors 37a and 37b, the position of the auxiliary transfer body 11can be guided with a directing valve 126.

A directing valve 128 controls via the pressurized medium connectors 65and 66 the cylinder-piston combination 61 in the stopper 3. Further, adirecting valve 129 controls the pressurized medium space 75 throughpressurized medium channel systems 73 and 74.

We claim:
 1. A sheet metal work center comprising:a body; a work tablewhereon a sheet to be worked is placed; means for holding and movingsaid sheet for work processing; upper and lower tools for respectivelyimpacting said sheet at its opposite sides; a releaser means positionedrelative to said upper tool; a locking arrangement being placed betweensaid upper tool and said releaser means; a transfer device for movingsaid upper tool and said releaser means in the vertical direction, saidtransfer device being arranged to have two parts; wherein, when saidsheet metal work center operates in a passive mode, said releaser meansis positioned a certain distance from the surface of said sheet, and themovements of said upper tool and said releaser means are made with saidlocking arrangement locked and with either part of said transfer devicebeing used; and wherein when said sheet metal work center operates in anactive mode, said releaser means is in contact with the surface of saidsheet, and the movements of said upper tool and said releaser means aremade with said locking arrangement locked and with either part of saidtransfer device being used.
 2. Sheet metal work center according toclaim 1, wherein the operation of said upper tool is conducted with saidlocking arrangement released and a first part of said transfer devicebeing used, and said releaser means being kept at its position by asecond part of said transfer device.
 3. Sheet metal work center of claim1, wherein the operation of said lower tool is conducted with saidlocking arrangement released, said releaser means being kept at itsposition by a second part of said transfer device, and said lower toolbeing driven to impact said sheet to effect forming thereto.
 4. Sheetmetal work center comprising:a body; a work table whereon a sheet to beworked is placed; means for holding and moving said sheet; upper andlower tools for respectively impacting opposite sides of said sheet; areleaser means positioned relative to said upper tool; a transfer devicefor moving said upper tool and said releaser means in the verticaldirection, said transfer device having two parts; and a lockingarrangement placed between said upper tool and said releaser means;wherein at least part of the vertical movements of said upper tool andsaid releaser means is implemented by using a part of said transferdevice, said upper tool and said releaser means being connected withsaid locking arrangement.
 5. Sheet metal center according to claim 4,wherein said sheet metal center is adaptable to operate in an activemode and a passive mode, said releaser means being positioned a givendistance from the surface of said sheet and said locking arrangementbeing locked so that the movements of said upper tool and said releasermeans are driven by either part of said transfer device when said sheetmetal work center operates in said passive mode, and said releaser meansbeing in contact with the surface of said sheet and said lockingarrangement being locked so that the movements of said upper tool andsaid releaser means are driven by either part of said transfer devicewhen said sheet metal work center operates in said active mode.
 6. Sheetmetal work center of claim 4, wherein the operation of said lower toolis conducted with said locking arrangement released, said releaser meansbeing kept at its position by a second part of said transfer device, andsaid lower tool being driven to impact said sheet to effect formingthereto.
 7. Sheet metal work center according to claim 4, wherein saidupper tool and said releaser means are placed in a buffer structurehaving a buffer fixing body, said buffer structure being mounted in saidbody of the sheet metal work center.
 8. Sheet metal work centeraccording to claim 4, wherein said transfer device comprises two parts,the first part of said transfer device being placed between a buffer, towhich said upper tool is fixed, and a buffer fixing body, and the secondpart of said transfer device being placed between an auxiliary transferdevice, to which said releaser means is fixed, and said buffer fixingbody.
 9. Sheet metal work center according to claim 8, wherein saidbuffer fixing body is a substantially tubular form piece havingpositioned therein a substantially tubular auxiliary transfer device,said buffer being inserted inside said auxiliary transfer device;andwherein said transfer device is adapted to conduct relative movementsbetween said buffer fixing body, said auxiliary transfer device and saidbuffer in the longitudinal direction of a buffer structure.
 10. Sheetmetal work center according to claim 9, wherein said locking arrangementis placed between the inner surface of said auxiliary transfer deviceand the outer surface of said buffer.
 11. Sheet metal work centeraccording to claim 8, wherein said locking arrangement comprises:anannular pressurized medium space formed between said auxiliary transferdevice and said buffer, said pressurized medium space holding a rotarypiston whose first radial surface faces the front surface of saidpressurized medium space in connection with said buffer and whose secondradial surface faces the front surface of said pressurized medium spacein connection with said auxiliary transfer device, wherein when themedium is pressurized between said auxiliary transfer device and saidsecond radial surface of said rotary piston, the moves of said auxiliarytransfer device being locked to said buffer, the front surface being inconnection with said buffer and in a power transmission connection tothe first radial surface of said rotary piston when the first part ofsaid transfer device is in operation.
 12. Sheet metal work centeraccording to claim 8, further comprising:an arrangement to be used asthe second part of said transfer device, wherein said buffer fixing bodyhas an inner surface provided with a recess in the longitudinaldirection of a buffer structure to which said buffer resides; andwherein the outer surface of said auxiliary transfer device beingprovided with a protruding flange to be placed in the recess, and saidbuffer fixing body being provided with pressurized medium connectors fordirecting the effect of the pressurized medium on opposite frontsurfaces of said flange.
 13. Sheet metal work center according to claim8, wherein said upper tool is positioned in a buffer structure, furthercomprising:a releaser transfer device placed between said auxiliarytransfer device and said releaser means for moving said releaser meansin the longitudinal direction of said buffer structure in relation tosaid auxiliary transfer device.
 14. Sheet metal work center according tothe claim 13, wherein said releaser transfer device comprises asleeve-like frame part surrounding said buffer, its lower part beingprovided with a clip for removably fixing said releaser means to a framepart and its upper part being provided with a protruding flange partplaced in the recess forming the pressurized medium space in theauxiliary transfer device, wherein a channel system penetrating theauxiliary transfer device and being in connection with the pressurizedmedium connector in the buffer fixing body is connected with the recess.15. Sheet metal work center according to claim 8, wherein a first partof said transfer device is placed in the upper part of a bufferstructure, and a second part of the transfer device is placed in thelower part of said buffer structure.